The present invention relates to novel dye compositions for dyeing cellulose acetate fibres, especially secondary acetate fibres and blends of secondary acetate fibres with other fibres both natural and synthetic.
Mixtures of disperse dyes are well known for the dyeing of synthetic fibres, particularly for polyester and for secondary celulose acetate fibres and their blends with other fibres.
Polyester fibres in particular are well served both in the inventive art of, and in the commercial availability of, disperse dye mixtures which provide navy and black shades with good application properties and good fastness to washing and to light. Many such mixtures based upon the mixture of two or more dyes of general structure (I), where X may be hydrogen or alkoxy, and R and Rxe2x80x2 may be alkl or alkenyl. Such mixtures are exemplified in, for example U.S. Pat. No. 5,393,308 (to BASF) and GB 1,582,743 (to ICI), and commercially provide economic navy and black shades of adequate fastness when applied to polyester. 
These mixtures, and many other mixtures which are based upon high energy dyes, are however unsuitable for the dyeing of secondary cellulose acetate.
It is an object of the present invention to provide novel disperse dye mixtures, based upon known dyes, which are especially suitable for the dyeing of secondary cellulose acetate.
Secondary cellulose acetate fibres are commonly used as linings on coats and suits. Dyeing of the fibres usually takes place at less than 100xc2x0 C. at atmospheric pressure in water. The main commercial acetate fibre dyes are black. However, very few companies offer good black dyes for acetate fibres.
Dyes of formula (II) and (III), as identified hereafter, are previously known dyes for the dyeing of synthetic fibres. The preparation of dye (II), and the use of the dye in the coloration of aromatic polyester textile materials is exemplified in example 1 of UK patent 1,394,367 (ICI). Commercial preparations of the dye are available and recommended for use on polyester fibres as Dispersol Blue XF (trade mark BASF) and Serilene Blue HWF (trade mark Yorkshire Chemicals). However, dye (II) has never to the applicant""s knowledge been used on acetate fibres before.
Dye (III) is disclosed in claim 5 and page 10 of UK Patent 1,112,146 (BASF) and is commercially available and recommended for use on polyester fibres as Palanil Dark Blue 3RT (trade mark BASF) and Serilene Dark Blue RT-LS (trade mark Yorkshire Chemicals). Two new (xcex2- and xcex3-) crystal forms of dye (III) are disclosed in UK patent 1,438,586 (BASF).
No previous use of the dyes (II) and (III) in admixture for the coloration of textiles has been found, and there is no suggestion in the prior art that (II) and (III) should be combined.
According to a first aspect of the present invention there is provided a dye composition for dyeing fibres comprising
(a) an azo dye of the formula (II): 
or a salt thereof, and
(b) an azo dye of the formula (II): 
or a salt thereof.
When referring to dyes (II) and (III) throughout the specification, the salts thereof are intended to be included. The same applies for dyes (IV) to (IX) define hereinafter.
The dye composition of the present invention is blue, and can form the basis of navy and black dye compositions for providing navy or black shades on, for example, secondary cellulose acetate fibres.
The dye composition is especially suitable for dyeing secondary cellulose acetate fibres. From the resultant dyeings, it has been found that the dye compositions of the present invention display fastness properties superior to those provided by dye compositions currently available for the provision of navy and black shades on secondary cellulose acetate. This superior fastness extends to blends of secondary cellulose acetate with other fibres, for instance with wool, viscose fibres and synthetic elastomeric fibres.
The exact shade achieved by the blue mixture or composition of the present invention may be changed by varying the proportions of the two dyes, and may be varied further by the addition of one or more further blue dyes to the dye composition.
Preferably, the dye composition comprises from 20% to 80% of dye (II) and from 20% to 80% of dye (III), by weight of the total amount of dyes (II) and (III) in the composition.
The BASF inventors of UK patent 1,438,586 claim that the xcex2- and xcex3-forms or modifications of the dye (III) disclosed therein have better stability under liquor dyeing conditions (100-200xc2x0 C., eg. up to 140xc2x0 C.) and better rheological properties than the xcex1-form (crystal form) or xcex1-modification of dye (III), which was previously known for dyeing of polyester and cellulose acetate. However, the present inventor has now found that, contrary to the indications in GB 1,438,586, the xcex1-form is actually superior for dyeing cellulose acetate (eg. secondary acetate) fibres giving a better rate of dyeing than the xcex2- and xcex3-forms of dye (III), so that a shorter time is required in the dye bath, and producing a more on-tone build up of the required navy or black shade on the fibres. Without being bound by theory, this quicker dyeing is thought to be because the xcex1- form of dye (III) has a greater solubility than the xcex2- and xcex3-forms in the dye bath at typical acetate dyeing temperatures of about 75-85xc2x0 C. This increased solubility in turn is probably because the xcex1-form of (III) is less thermodynamically stable and has a lower melting point and crystal energy than the xcex2- and xcex3-forms.
The xcex1-form of dye (III) has an X-ray diffraction graph (CuKxcex1radiation) having a characteristic line of strong intensity at a diffraction angle 2xcex8 of 25.50xc2x0, and lines of medium intensity at diffraction angles of 5.9xc2x0, 12.1xc2x0, 13xc2x0, 14.2xc2x0, 15.9xc2x0, 17.8xc2x0, 18.4xc2x0, 24.1xc2x0, 26xc2x0 and 28xc2x0.
Therefore, in a particularly preferred embodiment of the present invention, some or all of the dye (III) is present in an xcex1- form characterised substantially by the above X-ray diffraction graph. Preferably xe2x89xa750%, more preferably xe2x89xa780%, even more preferablyxe2x89xa795% and most preferably 100% of the dye (III) is present in the xcex1-form.
Alternatively, the dye (III) can comprise or can be present in, or some or all of the dye (III) can be present in, the xcex2-form and/or the xcex3=form of dye (III). The xcex2- and xcex3-crystal forms of dye (III) are disclosed in UK patent 1,438,586, and are characterised substantially by x-ray diffraction graphs (CuKxcex1 radiation) as follows:
xcex2-form: line of strong intensity at a diffraction angle 2xcex8 [xc2x0] of 25.3; lines of medium intensity at diffraction angles 2xcex8 [xc2x0] of 7.3, 13.6, 13.9, 16.7, 21.1, 23.1 and 29.0; and optionally lines of weak intensity at diffraction angles 2xcex8 [xc2x0] of 14.3, 18.3, 19.8, 22.6 and 26.1. xcex3-form: line of strong intensity at a diffraction angle 2xcex8 [xc2x0] of 24.5; lines of medium intensity at diffraction angles 2xcex8 [xc2x0] of 10.9, 18.3 and 22.3; and optionally lines of weak intensity at diffraction angles 2xcex8 [xc2x0] of 9.0, 17.8, 20.8, 23.2, 26.2, 27.6 and 28.0.
Optionally, the dye composition additionally comprises an azo dye of the formula (VI) and/or an azo dye of the formula (IX): 
or one or more salts thereof.
The dyes (VI) and (IX) are also blue and further vary the shade achieved by a basic blue composition containing dyes (II), (III) and [(VI) and/or (IX)] and no other dyes.
Preferably, the dye composition comprises from 20% to 70%, or more preferably from 30% to 60%, of dye (VI) or of dye (IX) or of the total weight of dyes (VI) and (IX), by weight of the total weight of dye (II) and dye (III) in the composition.
Other blue dyes may also be used in addition to or instead of dyes (VI) and (IX), and may be present in the same proportions as those preferred for (VI) and/or (IX).
Preferably, the dye composition comprises one or more additional dyes (preferably azo dyes) adapted to give the dye composition and/or fibres with which the composition comes into contact a black shade These dyes can include (i) yellow dyes, (ii) yellow-brown or brown dyes, (iii) orange dyes and/or (iv) red dyes, these dyes preferably being suitable for dyeing acetate. These additional dyes can be added to the composition of the invention in a manner familiar to those skilled in the art to convert the blue dye mixture into black mixtures which have superior properties for the dyeing of cellulose acetate fibres (e.g. secondary cellulose acetate fibres). Obviously, the exact tone of the black dye mixture derived, when dyed on cellulose acetate fibres, will depend upon the type, and proportions of the further dyes added.
More preferably, the one or more additional dyes can include the orange dye of formula (IV), the brown dye of formula (V), the red dye of formula (VII) and/or the yellow dye of formula (VIII), and/or a salt or salts thereof. 
The general principle of producing a black effect by colour mixture is well known, and is described in such texts as xe2x80x9cColorxe2x80x94An Introduction to Practice and Principlesxe2x80x9d, author R. G. Kuehni, [John Wiley and Sons Inc., 1997]. The application of this principle to dyestuffs mixtures is also well known, and is exemplified in the previously referenced U.S. Pat. No. 5,393,308 (BASF).
The dye composition preferably contains from 10 to 50% of dyes by weight of the total weight of the dry ingredients of the composition, and/or additionally contains from 50 to 90% of a dispersant or a plurality of dispersants by weight of the dry ingredients of the composition The dye composition may be required either as a solid or a liquid. The composition may thus contain between 0 and 90 wt % water. A lignin sulphonate may be used as a dispersant.
The novel dye compositions may also contain other non-dye components which, typically, enhance the dyeing properties of the dye compositions in the dyeing process. These components include, for example, lignin sulphonates and the products of sulphonation or sulphomethylation of the condensates of formaldehyde with aromatic compounds.
The essential components of the dye composition of the present invention can be prepared and/or obtained commercially as follows. Dyes (II) and (III) are previously known dyes for the dyeing of synthetic fibres. The dye (II) can be prepared by the method exemplified in example 1 of UK patent 1,394,367 (ICI). Commercial preparations of dye (II) are also available and recommended for use on polyester fibres as Dispersol Blue XF (trade mark BASF) and Serilene Blue HWF (trade mark Yorkshire Chemicals plc, Kirstall Road, Leeds, LS3 1LL, United Kingdom). Dye (III) is disclosed in claim 5 and page 10 of UK patent 1,112,146 (BASF) and is commercially available and recommended for use on polyester fibres as Palanil Dark Blue 3RT (trade mark BASF) and Serilene Dark Blue RT-LS (trade mark Yorkshire Chemicals). A prior art synthesis of the xcex1-form of the dye (III) is suggested in German patent No. 1,544,375; and a new improved synthesis is disclosed hereinafter.
The dye compositions may be prepared using conventional methods whereby the individual component dyes may be separately processed with the dispersing agent or agents, followed by the blending of the individually finished dyes in the required ratios. Alternatively, the dyes may be combined in the required proportions prior to processing (e.g. by adding the dispersing agent or agents).
According to a second aspect of the present invention, therefore, there is provided a method of making a dye composition according to the present invention, comprising mixing the dyes together, preferably in the stated weight ratios.
According to a third aspect of the present invention, there is provided a dye bath composition comprising a dye composition according to the present invention and water. Usually, the dye composition is dispersed in the water.
According to a fourth aspect of the present invention, there is provided a method of dyeing fibres comprising contacting fibres with a dye composition or dye bath composition of the present invention in a dye bath.
Preferably, the fibres comprise cellulose acetate fibres (more preferably secondary cellulose acetate fibres) or blends thereof with other natural and/or synthetic fibres such as wool, viscose, and/or synthetic elastomeric fibres.
Preferably, the dye bath is brought to a raised temperature after the fibres have been introduced into the dye bath. Preferably, after the fibres have been introduced into the dye bath, the dye bath is gradually heated to 60-95xc2x0 C., more preferably to about 75-90xc2x0 C., even more preferably to about 85xc2x0 C. In commercial operation the actual dyeing takes place in the jig or jet dyeing machine or the like when the fabric is only wetted with the dye liquor and the actual dyeing probably takes place at a temperature of about 10xc2x0 C. less than that of the dye bath.
Preferably, the fibres are left in the hot dye bath or machine until dyeing is substantially complete. This may take from one to eight hours depending upon the temperature and the type of machine used. The dye bath is then preferably gradually cooled (usually to 40-70xc2x0 C.) before removing the fibres, and preferably the fibres are then rinsed. The method is suitable for dyeing fibres in the form of textile fabrics.
The method of dyeing may also comprise later steps (after removing the fibres from the dye bath) of reduction clearing the fibre, rinsing the fibre, drying the fibre, and/or stentering the fibre.
According to a fifth aspect of the present invention there are provided fibres and/or a textile material dyed using a dye composition, dye bath composition and/or method of the present invention. Preferably, the fibres and/or textile material comprise cellulose acetate fibres (more preferably secondary cellulose acetate fibres) or blends thereof with other natural and/or synthetic fibres such as wool, viscose and/or synthetic elastomeric fibres.
According to a sixth aspect of the present invention, there is provided a method of making an xcex1-form of the dye (III) or a salt thereof as defined above, comprising the steps of:
(a) reacting 3-amino-5-nitro-2,1-benzisothiazole or a salt thereof with a diazotising agent, and
(b) coupling the diazotised benzothiazole with N-ethyl-N-[2-(methoxycarbonyl)ethyl]aniline or a salt thereof.
Preferably, the diazolising agent comprises nitrosyl sulfuric acid (e.g. formed in situ from sodium nitrite in sulfuric acid)
Preferably step (a) is carried out in a solvent which comprises sulfuric acid (e.g. xe2x89xa790% e.g. 95-99% sulfuric acid by weight of water present), and/or at a temperature of xe2x88x9220 to 5xc2x0 C., more preferably 0 to 5xc2x0 C. The preferred duration of step (a) is 3 to 4 hours.
Preferably, step (b) is carried out in aqueous medium.
Preferably, in step (b) the diazotised benzothiazole is added gradually (e.g. continually or batchwise) to a reaction vessel containing the N-ethyl-N-[2-(methoxy carbonyl)ethyl] aniline or the salt thereof. Preferably, the temperature is maintained at xe2x88x9210xc2x0 C. to 10xc2x0 C., more preferably xe2x88x925xc2x0 C. to 0xc2x0 C., during the gradual addition. The pH is preferably substantially maintained at 3-6, more preferably 4-5, during the gradual addition (e.g. by addition of base or alkali). After the gradual addition, the reaction mixture is acidified and preferably heated to  greater than 25xc2x0 C. More preferably 24 50% for a period of 10 minutes to 3 hours., more preferably for 60 to 90 minutes.
According to a seventh aspect of the present invention, there is provided a method of making a dye composition according to the first aspect of the invention comprising:
a) making an xcex1-form of the dye (III) or a salt thereof as defined above according to the sixth aspect of the present invention, and
b) mixing said xcex1-form of dye (III) or salt thereof with one or more dyes including dye (II) or a salt thereof.